Communication system for mobile users using adaptive antenna

ABSTRACT

A communication system has a base station having an adaptive antenna with a plurality of main array antenna elements for generating a plurality of communication beams. The system further includes a gateway station coupled to the base station. The gateway station forms a plurality of beams commands by communicating plurality of a control signals to the base station to form the communication beams.

RELATED APPLICATION

[0001] The present application claims priority to provisionalapplications Serial No. 60/266,684 filed on Feb. 5, 2001; Ser. No.60/262,717 filed on Jan. 19, 2001; and Ser. No. 60/262,701 filed on Jan.19, 2001; each of which are incorporated by reference herein. Thepresent application is also related to U.S. patent application entitled;“Multiple Basestation Communication System Having Adaptive Antennas”(Attorney Docket Number PD-201005); and “Stratospheric PlatformsCommunication System Using Adaptive Antennas” (Attorney Docket NumberPD-201015); filed simultaneously herewith and incorporated by referenceherein.

TECHNICAL FIELD

[0002] The present invention relates generally to a communication systemand more particularly, to a communication system using a ground-basedbase station and a gateway station that performs beam control at thegateway station.

BACKGROUND ART

[0003] In this communication age, content providers are increasinglyinvestigating ways in which to provide more content to users as well asinterfacing with users.

[0004] The Internet has increased the need for consumer information athigh speeds. DSL and cable modems are increasing in popularity becausethey provide higher byte rates than telephone and modem-based systems.Providing broadband access through cable or DSL service requiresincreased infrastructure. That is, cables must be laid through whichservice is provided. Cables are time consuming and costly to provide aswell as costly to maintain.

[0005] Because of high competition, cost for providing service is animportant factor. Also, providing high data rates is also an importantfactor.

[0006] Limitations to the number of users may be inhibited byinterference in systems. For example, for every beam having a main lobe,a parasitic number of side lobes exist which may cause interference withbeams using the same system resource such as frequency.

[0007] It would therefore be desirable to provide a mobile communicationsystem that is capable of rapid deployment, is easy to change, shouldthe technology inevitably change and reduces the amount of interferencewith adjacent beams to permit high throughput.

SUMMARY OF THE INVENTION

[0008] The present invention provides a communication system that allowsrapid deployment and provides interference rejection. The presentinvention is suitable for both fixed users such as those positioned in abuilding or home or for mobile users.

[0009] In one aspect of the invention, a communication system has a highaltitude device having an adaptive antenna with a plurality of mainarray antenna elements for generating a plurality of communicationbeams. The system further includes a gateway station coupled to the highaltitude device. The gateway station forms a plurality of beams commandsby communicating plurality of a control signals to the high altitudedevice station to form the communication beams.

[0010] In a further aspect of the invention, a method of controlling acommunication system comprises the steps of:

[0011] dividing a communication signal into a plurality of multipledynamic links at the gateway station;

[0012] directing the multiple dynamic links to a plurality of basestations; and

[0013] coupling the multiple dynamic links through the plurality of basestations.

[0014] One advantage of the invention is that due to the interferencedetection, system throughput is increased over conventional systems.

[0015] Another advantage of the invention is that by locating a majorityof the processing remote from the base stations, overall costs ofsystems may be further reduced.

[0016] Other features and advantages of the present invention usingremote digital beam forming are readily apparent from the followingdetailed description of the best mode for carrying out the inventionwhen taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a system diagram of a communication system according tothe present invention.

[0018]FIG. 2A is a top view of a base station antenna according to thepresent invention.

[0019]FIG. 2B is a side view of the base station antenna of FIG. 2A.

[0020]FIG. 2C is a side view of a panel of the base station of FIG. 2Aillustrating elements thereon.

[0021]FIG. 2D is an alternative side view showing elements of a panel ofa base station.

[0022]FIG. 2E is a third alternative embodiment of elements of a panelof an antenna according to the present invention.

[0023]FIG. 3 is a high level block diagrammatic view of element modulescoupled to a data bus.

[0024]FIG. 4 is a beam pattern for the panel illustrated in FIG. 2.

[0025]FIG. 5 is a block diagrammatic view of a digital beam formingcircuit according to the present invention.

[0026]FIG. 6 is a block diagrammatic view of a beam forming circuitusing noise injection according to the present invention.

[0027]FIG. 7 is a block diagrammatic view of a base station processingcircuit according to the present invention.

[0028]FIG. 8 is a block diagrammatic view of a gateway processingstation according to the present invention.

[0029]FIG. 9 is a more detailed schematic view of a demultiplexing beamforming and nulling circuit according to the present invention.

[0030]FIG. 10 is an alternative for the remote processor; an adaptivedigital beam forming and nulling processor according to the presentinvention.

[0031]FIG. 11 is an alternative nulling circuit with a limiter on thefeedback path according to the present invention.

[0032]FIG. 12A is an output of a digital beam forming circuit notincluding limiter as shown in FIG. 10.

[0033]FIG. 12B is an output of the circuit of FIG. 10 with limiters atall feed-through paths.

[0034]FIG. 12C is an output of circuit shown in FIG. 11 with limiter onthe feed-back path, wherein the power density levels of both the weakand strong interference is successfully reduced below a threshold.

[0035]FIG. 13 is an alternative digital beam forming and nullingprocessor using auxiliary elements.

BEST MODES FOR CARRYING OUT THE INVENTION

[0036] In the following description, the same reference numerals areused to identify the same components in the various views. Those skilledin the art will recognize that various other embodiments, structuralchanges and changes in measures may be made without departing from thescope of the invention. The teachings of the present invention may beused for both fixed users as well as mobile users.

[0037] Referring now to FIG. 1, a communications system 10 has aplurality of beams 12 that are illustrated as a plurality of circles 14on the earth's surface. Circles 14 represent the footprint of a radiatedbeam onto the earth's surface. A plurality of user terminals 16M and 16Fare used to illustrate mobile users and fixed users, respectively.Mobile users 16M may comprise but are not limited to automotiveapplications, personal digital assistant applications and cellular phoneapplications. Fixed user terminals 16F may, for example, comprisebusiness-based or consumer-based communication systems. Each userterminal 16F and 16M may receive a signal with the predetermined signalstrength from a communication beam or communication beams throughmultiple links from one or more base stations 18. The present inventionis particularly advantageous for use with mobile terminals 16M. Althoughonly two wireless basestations are illustrated, they may each representa plurality of basestations.

[0038] Communication system 10 further includes a gateway station 20that is coupled to terrestrial networks 22. Gateway station 20 may becoupled to a base station processing center 24. Gateway station 20provides a links between user terminals 16F, 16M and terrestrialnetworks 22 through base stations 18. Gateway station 20 may be coupledto terrestrial networks 22 such as the public service telephone network,the Internet, or an intranet. Although illustrated as two separateunits, gateway station 20 and processing center 24 may be combined intothe same physical location.

[0039] The communication signals between base station 18 and userterminals 16M and 16F may be referred to as user links 26. User links 26represent the transmit and receive beams from both categories of userterminals 16F, 16M and base station 18. A feeder link 28 is definedbetween base station 18 and gateway station 20.

[0040] Base stations 18 are used as a communication nodes for gatewaystation 20 and user terminals 16F and 16M. For communicating with userterminals 16M and 16F, base stations 18 have an adaptive antenna 30formed of panels of reconfigurable elements as will be further describedbelow. Each base station 30 also has a directional antenna 32 forcoupling to gateway station antenna 34. The coupling of antennas 32 and34 allows base station 18 to be wireless and therefore advantageously beeasily deployed. As will be described below, the pointing from bothmobile terminals 16M and base station 18 may be performedelectronically. Although only one gateway station 20 is illustrated inthe figure, those skilled in the art would recognize that variousnumbers of gateway stations may be employed. Gateway station 20 has agateway control circuit 23 that controls the content and communicationwith the base station 18.

[0041] Base station 18 has a controller 36 that links user terminals16M, 16F through antenna 32 with gateway station 20. In the presentexample, the controller 36 is used in the return link direction tomultilplex received signals from all the array element into the feederlink signals 28 as determined in the gateway station 20. Similarly inthe forward link direction, controller 36 is used to de-multiplex thefeeder link signals into various streams of signals for array elementsto transmit.

[0042] Gateway control circuit 23 may have various circuitry coupledthereto. For example, analog or digital TV 38, an up converter 40, and acable modem terminal shelf (CMTS) 42. CMTS 42 may be used to couple toterrestrial networks such as Internet 22. CMTS 42 may be coupled to ahub 44 that has various resources coupled thereto. The hub 44 may, forexample, have a management server 46, a world wide web, e-mail or newsserver 48 or a proxy server 50.

[0043] Referring now to FIGS. 2A, 2B, 2C, and 2D, antenna 30 is shown infurther detail. In the illustrated embodiment, antenna 30 has fivepanels 52 that are used to direct communication signals to a desireddirection. As is illustrated best in FIG. 2A, each panel 52 has a fieldof view and a scanning range slightly narrower than the field of view.Each panel is preferably a flat panel that allows cost effectivemultiple connectivity from base station 18 to the various users. Eachpanel 52 is used to establish multiple dynamic links. In combination,the various base stations together are used to form the communicationsignal with the users. Thus, multiple base stations through multiplepanels 52 of antennas 30 are used in each communication. The bandwidthon demand is accomplished not by a variety of data rates via a single rflink but through different data rates resulting from variouscombinations of multiple dynamic rf links. As will be further describedbelow, as the user moves, some links may fade away while new links maybecome available. Thus, multiple links will always be connected to auser. As illustrated, five panels are used, however, those skilled inthe art will recognize various numbers of panels may be used.

[0044] As is best shown in FIG. 2B, panels 52 have an angle 54 relativeto the horizontal. Angle 54 allows the communication signals generatedat panels 54 to be directed slightly downward toward the earth'ssurface. Of course, angle 54 depends on the height of base station 18above the earth's surface. That is, as the height of the towerincreases, the angle 54 decreases. The angle is such to give a desiredservice area for each panel 52.

[0045] In operation, the combination of simultaneous multiple beamcapability on both the mobile terminals and base stations will makeoverall mobile systems even more cost effective. A user through theirassociated multiple beam user device or appliance will connect to an IPnetwork by establishing multiple dynamic links through various basestations to the communication nodes of the Internet. As a result,precious mobile spectrum may be reused many times when mobilesubscribers use directional antennas. The same amount of spectrum can beused again and again to increase the bandwidth density (i.e., totalbandwidth a mobile system can project into a unit area). Therefore, thesystem will provide more throughput for users and larger capacity forthe operators, and more efficient utilization for regulators. Providinga high gain on both user terminals and base stations allows the cellsize to be extended extensively without impacting the bandwidth density.The bandwidth on demand will be implemented through multiple dynamiclinks and thus multiple links will always be available to a user. Theremay be many bases stations within a field of view of a mobile user. Forexample, there may be as many as between five and ten bases stationswithin a user's field of view. A user with an omni directional terminalmay connect to one nearest base station with an rf channel (specified byfrequency, time and/or code). This channel will not be assigned to otherusers as in a conventional cellular system. Adaptive antennas on basestations allow operators to use the same channel again within the same“cell” but via different base stations, provided the base stations havethe capability to directionally discriminate against interferences atthe same channel as that intended user but at different directions. Aswill be further described below, the user and interference sources mustbe located reasonably far to make the adaptive technique effective. Thebase stations may include circuitry to null or offset interferencesbetween the communication signals. During an acquisition phase, e.g.,from a cold start, all received beams will be “on” to cover the entirefield of view of a fan beam. Thus, the various beams will have differentelevation angles and azimuth angles to cover the search volume. Once auser link is established, only nearby beams from a particular panel 52may be activated.

[0046] Once a user link is established, the tracking mechanism uses atype of step scan principle. The signal strengths from adjacent receivedbeams will be monitored and compared with one coming from the main beam.The beam with the strongest signal will be identified as a “locked” ormain beam. As a user moves, the tracking base station may switch (i.e.,step) a received beam from one position to an adjacent one with thestrongest signal, and assign the transmit beam accordingly.

[0047] As is best shown in FIG. 2C, a panel 52 may be comprised of aplurality of radiation elements or patches 56. Radiation elements 56may, for example, be described as a “patch array.” As is illustrated, 90elements are illustrated in FIG. 2C. Each element 56 has a diameter of0.3 wavelengths. Element modules are placed at slightly less than 0.7wavelengths apart in a nearly square lattice. Panel 52 may also bereferred to as an “aperture.” Panel 52 has a radiating area in the orderof about 25 square wavelengths. The expected peak gain of a beam is 24dB at the boresight, and about 22 dB at 45 degrees away from theboresight. Beam widths for the boresight elliptical beam is about 10degrees in azimuth and 15 degrees in elevation respectively. The beamsare dynamic and therefore assigned to track individual subscribersaccordingly.

[0048] Referring now to FIG. 2D, a 45 element panel 52 is illustrated.Such a panel has about 3 dB less gain than that of the panel illustratedin FIG. 2C while maintaining about the same directional discrimination.

[0049] Referring now to FIG. 2E, another element configuration of a flatpanel 52 is illustrated for a high frequency application. In thisembodiment, panel 52 has about 36 elements. In this embodiment, eachelement is approximately 0.6 wavelengths in diameter with elementspacing slightly less than 0.7 wavelengths apart in a nearly squarelattice. The total aperture has a rating area in the order of about 10square wavelengths. The peak expected gain of the beam is about 20 dB atboresight and 18 dB 45 degrees away from the boresight. The beam widthsfor the boresight elliptical beam are about 5 degrees in azimuth and 15degrees in elevation, respectively. Therefore, at 2 kilometers away fromthe base station, the beam width and azimuthal direction is about 200meters. Of course, fewer elements may be used depending on thefrequencies involved. That is for higher frequencies because more datais transferred, less elements may be required to match the processingpower of the circuitry.

[0050] For each of the above embodiments, long baselines, not fullapertures, over a large bandwidth provide good directionaldiscrimination capability. The thin array at a single frequency willexhibit high side lobes or semi-grading lobes. Over a large bandwidth,side lobes arise at various directions at different frequencycomponents. As a result, the integrated interference contribution fromside lobes over a large bandwidth tends to smear out or cancel while thecontribution to the main lobe over the same bandwidth may beconstructively added together. As will be further described below,additional cancellation schemes may be applied to reject interferencesfor all beams tracking to various subscribers if necessary.

[0051] Referring now additionally to FIG. 3, radiating elements 56 formmodules 58 which are plugged into panels 52. Panels 52 serve as backplates which are interconnected through a bus 60. Bus 60, for example,may include a DC power line 62, an inflow data line 63, an outflow dataline 64, an address line 65, and a control line 66. Panels 52 may bemodularized and include sockets for easy connection and disconnection ofmodules 58. Each panel or back plate 52 may include a processor 68 tohandle beam configuration. Processor 68 may be part of controller 36described above in FIG. 1.

[0052] Referring now to FIGS. 2E and 4, a beam pattern 69 for the panelof FIG. 2E is illustrated. The pattern 69 has circles 70 or ellipsesrepresenting beam positioning patterns from a dynamic beam allocationand positioning scheme, while the hexagon 71 representing fixed beampositions from a conventional static cell system. Panel 52 converts thereceived microwave power into a digital stream in the receivingdirection and converts the digital stream into radiated microwave powerin the transmitting direction. The phasing of various elements isimplemented by digital multiplication in a separated digital beamformer. The digital beam forming approach eliminates the need ofconventional phase shifters and minimizes required rf components, makingpossible a low cost implementation suitable for the consumer market.

[0053] Referring now to FIG. 5, a digital beam forming circuit 72 isillustrated for a base station (of FIG. 1). However, a similar beamforming circuit may also be used for a user device. Also, a receive beamforming network is shown, however, those skilled in the art willrecognize a corresponding transmitting beam forming circuit may beformed in reverse.

[0054] Digital beam forming circuit 72 has a plurality of elements 74.Various groupings of elements 74 are used to generate the simultaneousmultiple links of the present invention. Each element 74 is coupled to acorresponding analog-to-digital converter. As those skilled in the artwill recognize, a band pass filter (not shown) may also be coupledbetween element 74 and analog-to-digital converter 76. The digitaloutputs from all of the analog-to-digital converters 76 are weighted andsummed, then grouped together to form beams 1 through M as illustrated.The beams are formed by numerical multiplications using the directionvector beam 1 as illustrated as reference numeral 78 and throughdirection vector beam M as illustrated by reference numerals 80 throughforming circuit 82. Forming circuit 82 may have a plurality ofmultiplication blocks 84 and summing blocks 86 either implementedphysically or in software to form the various beams. Functions of beamforming, frequency tuning and time synchronization are interlaced tominimize the over processing mode, instead of sequentially. Thisapproach eliminates conventional phase shifters and minimizes therequired rf components making the implementation suitable for consumerapplications. Digital beam forming circuit 72 is used to generatemultiple simultaneous links with base station 18. The digital beamforming circuit 72 is configured such that a unique beam is assigned foreach individual user. The base stations will track users with uniquechannels and beam positions. Every user will have a bubble which is thebeam size associated with the assigned beam. The bubble forms anexclusion zone associated with each user for a specific channel. Usersassigned with the same channel can co-exist in a network as long astheir associated bubbles do not intercept one another. When bubbles fora particular channel collide, one user is assigned a new channel.

[0055] Direct samplings are used to simplify the architecture. Low costis achieved by the use of an analog-to-digital converter 76 that allowsanalog-to-digital conversion of the received signals at rf directlyallowing other processing to be performed digitally. High speed and lowspeed analog-to-digital conversion will over sample the receivedsignals. In one constructed embodiment, a user signal is assumed to beabout 5 MHz but could go as high as 30 MHz. A sampling rate was chosento be about 20 MBps per second with approximately a 4-bit resolution.Aperture time of the analog-to-digital converter must less thanone-eighth of the period of the carrier frequency. Therefore, at a 2 GHzcarrier frequency, the aperture time of about 50 picoseconds isadequate.

[0056] Referring now to FIG. 6, an alternative to the circuitconfiguration of FIG. 5 is illustrated. In this embodiment, the numberof analog-to-digital converters is reduced and the dynamic rangerequired for the individual analog-to-digital converters is alsoreduced. In the circuit of FIG. 6, element 74 may be weighted in block88 before a summer 90. Summer 90 is used to group a number of elementstogether. Each summing block 90 has an analog-to-digital converter 92associated therewith. Thus, by grouping a number of elements togetherwith a summing block 90, the number of analog-to-digital converters isthus reduced. Each summing block 90 may also be connected to a noiseinjection circuit 94. Structured noise may be added to the summing block90. The structured noise may consist of orthogonal codes. A similartechnique is described in U.S. Pat. No. 5,077,562 which is incorporatedby reference herein.

[0057] Each analog-to-digital converter 92 is coupled to demultiplexer96. Demultiplexer 96 is coupled to digital beam forming and interferencerejection network 98. Demultiplexer 96 demultiplexes the outputs fromanalog-to-digital converters 92 and provides them to digital beamforming and interference rejection network 98. Digital beam forming andinterference rejection network provides a received signal to beprocessed by the processing center.

[0058] Referring now to FIG. 7, a similar embodiment to that shown inFIG. 6 above is illustrated. In this embodiment, a portion of thecircuit may be located in base station while the remaining portion ofthe circuit may be located in a processing center. By removing some ofthe circuitry from a base station, a less costly and more flexiblesystem may be obtained. The same reference numerals are used for thesame elements in FIG. 7 as in FIG. 6. Elements 74 are coupled toweighted block 88 which in turn are coupled to summers 98. A weightedblock 100 is used after summer to couple summer 90 with a centralsumming block 102. The signal from summing block 102 is thus broadcastor transmitted to the gateway station for further processing.

[0059] Referring now to FIG. 8, a gateway portion 104 of the circuitillustrated in FIG. 7 is illustrated. A demultiplexer 96 similar to thatillustrated above is used. Demultiplexer 96 demultiplexes the broadcastsignal from summer 102 and provides it to an analog-to-digital converter106. Analog-to-digital converter 106 may be coupled to noise injectioncircuit 108. Noise injection circuit 108 may be similar to thatdescribed above in that noise injection circuit 108 may use orthogonalcodes. The output of analog-to-digital converter is provided to ademultiplexer portion 108 which in turn is coupled to digital beamforming and interference rejection network 98 similar to that in FIG. 6.Thus, digital beam forming network and digital interference rejectionnetwork provides received signals from the various beams. By providingthe demultiplexing analog-to-digital conversion and noise injection allin one location such as the gateway station, the complexity of the basestations may be reduced. Further, the number of elements provided at abase station may be increased due to the remote processing of the beamsignal.

[0060] Referring now to FIG. 9, a more detailed processing scheme for aCDMA system, such as 3rd generation mobile, from that shown in FIGS. 8is illustrated. In this embodiment, a diplexer 110 is connected to aradiator (not shown) so that both transmit and receive signals arethrough the same radiator. Only the receive functions are illustrated.The corresponding transmit functions are identical but in a reverseddirection. The received multiplexed signals are coupled to ananalog-to-digital converter 112. To simplify the block diagram, we didnot include the noise injection portion in here. Followinganalog-to-digital converter 112 a element code despreading circuit 114has a plurality of multiplication blocks 116 which performs the matchedfilter function via a multiplication 116 and a band pass filter 118, torecover the signal received at a specific array element in digitalrepresentation. Therefore at the outputs of the de-spreading block 114,the received signals of all the array elements at the remote basestations have been re-generated in digital forms. The regeneratedsignals are available for further processing.

[0061] A scheme in which every user will have a dedicated beam isillustrated. The received element signals by user codes are sortedelement by element before beam forming. More than one user per code isused but they come from different directions and arriving at differenttime.

[0062] Element code despreading circuit 114 is coupled to a user codedespreading circuit 120. Each user code is used to group multiple userswith the same user code together in user code despreading circuit 120.Different users may only be separated via time delay and direction ofarrival. Thus the block 120 must provide digital streams with multipletaps to beam forming network so that the user signals with the same usercode can be separated via time and directional “filtering processes.”Each user code from user code despreading circuit 120 is coupled todigital beam and null forming network. One digital beam and null formingnetwork is provided for each user. Track files 124 provide input todigital beam forming and null forming network 122. Track files includeinformation such as the user code, the location, timing and orientationof the users. Track files allow the communication signals to be dividedinto several links for communication through a number of base stations.The user signals after digital beam forming are output and coupled tosuch things as the Internet. Feedback is provided from output 126through an extended Kalman filter. The extended Kalman filter 128 isused to update each user position channel and potential for interferenceor collision with neighbors. The information from the extended Kalmanfilter 128 will be used to track the corresponding user.

[0063] Referring now to FIG. 10, an adaptive nulling circuit 130 thatcould be used with any of the circuits in FIGS. 7 through 9 isillustrated. For example, the circuit 142 of FIG. 10 may be implementedas a part of element 122 of FIG. 9. Circuit 130 has elements 132 whichare coupled to a beam forming circuit 134 and an analog-to-digitalconverter 136. Of course, as mentioned above, this portion of thecircuit may be similar to that shown in FIGS. 7 through 9. Amultiplication block 138 and amplifier 140 may also be included in thecircuit. A digital beam forming and nulling processor 142 is coupled toeach analog-to-digital converter. Each signal is multiplied by a weightat multiplication block 144 prior to being summed at a summer 146. Theoutput of summer 146 is the output signal Y(t). In a typical digitalbeam forming, the directional vector (the multiplier set) ispre-determined by pointing direction only, and usually will exhibit alinear phase progression on the array apertures for spot beams .However, in the adaptive beam forming and nulling network illustrated,the directional vector will be further modulated by signal environment,such that a beam is directed toward desired user while nulls are steeredtoward high interference directions. As a result the received signal tonoise (including interference) ratio is “maximized.” Negative feedbackblock 147 is provided from output signal Y_((t)) to a multiplicationblock 148 for each signal. The multiplication block 148 multiplies theinput signal from each analog-to-digital converter with the outputsignal Y_((t)). A sum through summer block 150 is provided to a weightupdate block 152. Weight update block 152, thus in response to themultiplication block 148, updates the weights and provides those tomultiplication blocks 144. The output is thus,

Y(t)=Σ₁ W _(y) Ŝ _(t)(t)

[0064] $\frac{w}{t} = {{- \alpha}{\nabla_{w}ɛ}}$

(∇_(w)ε)₁=2(y(t)−d(t)*S ₁(t))

[0065] Our method for adaptive nulling to use a least mean squarecriteria for steady state solution. In addition, a steepest descenttechnique may be used to reach the steady state solution. An indirectcorrelation technique is used, rather than a direct perturbationtechnique, to measure the “gradients” for each update.

[0066] Referring now to FIG. 11, to reduce cost and enhance the nullingefficiency, a limiter may be placed in the feedback path similar to thetechniques described in U.S. Pat. No. 4,635,063, which is herebyincorporated by reference. Limiting circuit 160 includes elements 162similar to those described above. Each element has an associated mainchannel 164, a feedthrough path 166, and a feedback path 168. Since thecircuitry associated with the respective elements are essentially thesame, the circuitry associated with only one sensor is referenced indetail. The function blocks can all implemented in digital format. ForInstance, power dividers correspond to data bus, weight circuits tomultipliers, correlators to processors combining multipliers andintegration-&-dumps, outputs of hard limiters to sign bits, and so on.

[0067] Correlators 170 co-process signals in the feedthrough path 166and feedback path 168; the result is transformed according to analgorithm by a computer 172. The weighting circuit 174 thusprogressively modifies the signal in the main channel 164 to minimizeinterference with a desired signal.

[0068] A limiter 176 is placed along feedback path 168. As explainedbelow, this placement simplifies correlator design relative to thecircuit without such limiters and improves performance relative toadaptive antennas with limiters in the feedthrough path.

[0069] Each element 162 is connected via the respective main channel 164to respective input power divider 180 or other means for dividing aninput signal between a pre-processed signal and a diagnostic signal. Adiagnostic signal is conveyed along the respective feedthrough path 166;the pre-process signal is conveyed along a second portion 182 of therespective main channel 164.

[0070] The amplitude and phase of pre-process signals may be modified byweighting circuit 174 or other weighting means associated with each ofthe elements 162. The resulting weighted signals are directed along athird portion 184 of respective main channel 164 to be summed by meanssuch as a power combiner 186. Means such as an output power divider 188inserted along a unified portion 190 of main channel 14 between thepower combiner 186 and antenna output 192, divides the summed signalbetween an output signal and a feedback signal.

[0071] The illustrated feedback path 168 includes means for eliminatingfrom the feedback signal the desired band of frequencies associated withthe primary signal source to be received by circuit 160. This means mayinclude a hybrid 194 for subtracting the desired band from a portion ofthe summed signal. More particularly, hybrid 194 includes a primaryinput 196 and a secondary input 198. The primary input 196 receives aportion of the summed signal from output power divider 188. Thesecondary input 198 receives only the part of the summed input with thedesired band. The desired band may be provided by means of a band passfilter 200, the input of which is a portion of the summed signaldirected thereto by output power divider 188. The output of hybrid isthe summed signal less the desired band. The elimination of the desiredband from the feedback signal avoids possible nulling against thedesired signal source. The limiter 176 is located in feedback path 168so that limiting occurs prior to division of the feedback signal. Thus,the need for plural limiters is obviated. Preferably, limiter 176 is ahard limiter. Ideally, a hard limiter transforms a sinusoidal input to asquare wave output.

[0072] The limited feedback signal is divided by means such as powerdivider 202 to provide feedback signals to provide feedback inputs 204of correlators 170. The feedback signal is correlated with thediagnostic signal received at feedthrough input 206 of each correlator170. The preferred correlator 170 is a multiplier coupled with a lowpass filter.

[0073] Each correlation resultant is transformed according to analgorithm by computer or processor 172 or alternative means. Thetransform is used to determine the weighting function of the weightingcircuit 174 or other weighting means. Preferably a gradient descentalgorithm such as least means square error, Howell-Applebaum powerinversion, is used.

[0074] Some of the advantages of the present invention can be betterunderstood in accordance with the following theoretical analysis. Thefunction of the ideal hard limiter is to produce a high constant levelpositive output whenever the input is positive and a low constant levelnegative output whenever the input is negative. The transition betweenthe constant positive and negative output values (or the thresholdvalues) is a sharp or discontinuous one. Therefore, with a sinusoidalinput the output would ideally be a square wave. In a multiple signalenvironment where the signal power differences are large (e.g., morethan 10 dB), the limiter will suppress weaker signals and enhance thestrongest signal. Qualitatively, the limiter will only respond to thestrongest signal.

[0075] In a phased array geometry, each element shares the same field ofview as every other element. Therefore, each element plays a nearlyequal role in forming a single beam. All jamming signals in the field ofview are sensed by every single element in the phased array.Consequently, the positioning of the limiter in either the feedthroughpath or the feedback path is critical for multi-interference rejectionin the phased array.

[0076] If the limiter is placed in the feedthrough path, its output willhave merely the information of the strongest interference, and theantenna system will null against the strongest interference accordingly.The correlator outputs will not include any of the other interferencesignal information to allow the antenna system to form nulls in theirdirections.

[0077] Alternatively, when a hard limiter is placed in the feedbackpath, the antenna system can first null against the strongestinterference signal until it becomes comparable to the second strongest.The antenna system will then null against both until the antenna systemreaches an inherent threshold level, created by quantization error orfeedback loop gain, limiter, etc.

[0078]FIG. 12 shows a comparison of the interference suppressionperformance and the convergence rate of three four-element phased arrayconfigurations: (a) no limiter, (b) limiters in the feedthrough path,and (c) limiter in the feedback path. These results were obtained from acomputer simulation program, ADAPT and are the dynamic spectral outputversus the number of iterations of the adaptive process.

[0079] As the adaptive process proceeds from the initial state in theconfiguration with no limiter, the strongest interference ismonotomically reduced until it is below the threshold value at iteration37, as show in FIG. 12A. The threshold value is set 35 dB below thestrongest interference. The weaker interference was not a driving forceuntil iteration 34. At this point, the weaker interference is slowly butcontinuously suppressed. At iteration 126, the interference signal isbelow the threshold value. During the adaptation, the desired signalpower density at the output is continually being enhanced until itreaches a steady state value of 10 dB above the threshold at iteration134. The system configuration works but it needs high dynamic rangecorrelators. In order to reduce high dynamic requirement on correlators,limiters are incorporated in the many modified options, as shown below.

[0080] In the configuration with the limiter in the feedthrough path,the power density level of the stronger interference is successivelyreduced below threshold but the power density level of the weakinterference increases initially and remains at that steady state valueas shown in FIG. 12B. The desired signal increases slightly in value,but is never enhanced above the weak interference. This system does notrespond adequately to the weaker interference signals.

[0081] In the configuration with the limiter in the feedback path, thepower density levels of both the weak and strong interference aresuccessfully reduced below the threshold as seen in FIG. 12C. Ascompared to the configuration with no limiter, the weaker interferenceis suppressed slightly faster. The weak interference is below thresholdat iteration 87. Throughout this process, the desired signal iscontinuously enhanced.

[0082] In accordance with the above, it can be seen that the presentinvention provides for improved performance over the no-limiter andlimiter in the feedthrough path designs of the prior art. The presentinvention further improves on the feedthrough limiter version byrequiring only one limiter, and improves upon the no-limiter version inrelieving the design requirements on the correlators.

[0083] Referring now to FIG. 13, another circuit 220 to provide nullingis illustrated. In this embodiment, a plurality of main array elements222 and auxiliary elements 224 is illustrated. Main array elements 222are similar to the elements described in the previous circuit. Auxiliaryelements 224 have been added to provide canceling of side lobes from themain elements. This will provide the capability to allow users to becloser together without interference. Main array elements 222 arecoupled to a main digital beam forming circuit 226. Auxiliary elements224 are coupled to an auxiliary digital beam forming circuit 228. Asumming block 230 sums the signals from the main array elements throughmain digital beam forming circuit 226 with weighted portions ofauxiliary elements to cancel interference. Feedback is provided througha weight update block 232. Weight update block 232 generates a weightfor each of the user signals and provides them to a multiplication blockwhere they are combined with the output of auxiliary digital beamforming circuit 228. The output of digital beam forming circuit may alsobe coupled to weight update block 232 to allow the weights to be formedas a function of the auxiliary digital beam forming input. The weightedauxiliary digital beam forming signals are combined in a summer 234where they are combined with each of the auxiliary digital beam formingcircuits and provided summer 230 for providing interferencecancellation. Thus, output 236 of circuit 220 has the main user signalsinterference compensated for by the auxiliary elements 224.

[0084] In operation of FIG. 13, main array elements 222 are used togenerate the communication beams of the present invention. The auxiliaryelements 224 are used to cancel interference from the main arrayelements as needed. That is, by using the positions of the users,weights may be determined for auxiliary elements 224 so that theauxiliary elements 224 will have an auxiliary element output to cancelinterference from the communication beams because of the direction ofstrong interfering sources for each active beam may be determined fromthe user position. Preferably, this is performed in the gateway stationto prevent complexity in the base station. As those skilled in the artwill recognize, it is the side lobes of the main beam that are to becanceled. By providing the auxiliary elements, the side lobes of themain beams may be reduced or selectively canceled by the auxiliaryelement outputs. Each panel described above may include canceling of theside lobes using auxiliary elements.

[0085] Advantageously, by providing the digital beam forming in thegateway station, all of the beams are formed in a real time manner usingthe user position files that exist in the gateway station. As the systemneeds change, the gateway station may adaptively change the output ofthe auxiliary elements on a continual basis.

[0086] While the best modes for carrying out the invention have beendescribed in detail, those familiar with the art to which this inventionrelates will recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

What is claimed is:
 1. A communications system comprising: a basestation having an adaptive antenna with a plurality of main arrayantenna elements for generating a plurality of communication beams; anda gateway station coupled to said base station, said gateway stationforming a plurality of beams commands by communicating a plurality ofcontrol signals to the base station to form the communication beams. 2.A communications system as recited in claim 1 wherein said adaptiveantenna comprises a plurality of panels comprise the plurality of mainarray elements.
 3. A communications system as recited in claim 1 whereinsaid base station comprises a plurality of auxiliary elements forcanceling interference between the communication beam.
 4. Acommunications system as recited in claim 1 wherein said auxiliaryelements are weighted to provide interference canceling.
 5. Acommunications system as recited in claim 1 wherein said gateway stationis rf coupled to said base station.
 6. A communications system asrecited in claim 1 wherein said base station is wireless.
 7. Acommunications system as recited in claim 1 wherein said gateway stationis positioned on a stratospheric platform.
 8. A communications system asrecited in claim 1 wherein said reconfigurable antenna comprises aphased array antenna.
 9. A communications system as recited in claim 1wherein said main array is a modular.
 10. A communications system asrecited in claim 1 wherein said main array comprises a plurality ofmodules coupled to a bus.
 11. A communications system as recited inclaim 1 wherein said bus is coupled to a controller.
 12. Acommunications system as recited in claim 1 further comprising aplurality of users receiving said communications beam.
 13. Acommunications system as recited in claim 1 further comprising a limitercoupled within a feedback path.
 14. A communications system as recitedin claim 1 further comprising a nulling processor.
 15. A communicationssystem as recited in claim 14 wherein said nulling processor comprisesan element code despread and a user code despread.
 16. A communicationssystem as recited in claim 15 wherein said nulling processor comprises aweighted feedback loop similarly coupled to an output signal.
 17. Acommunications system as recited in claim 15 wherein said nullingprocessor comprises auxiliary elements coupled to an output signal. 18.A communications system as recited in claim 1 wherein said base stationcomprises a plurality of summing blocks coupled to said main arrayelement for generating a summed signal, said gateway station comprisingan analog-to-digital converter coupled to a noise injection circuit andsaid summed signal, said summed signal coupled to a demultiplexer and adigital beam forming circuit.
 19. A communication system as recited inclaim 1 wherein said base station comprises a user code despreadingcircuit coupled to an element code despreading circuit which is coupledto said main array elements.
 20. A communications system comprising: aplurality of wireless base stations having adaptive antennas with aplurality of main array antenna elements for generating a plurality ofcommunication beams; a gateway station coupled to said plurality ofwireless base stations through a plurality of multiple dynamic links,said gateway station forming a plurality of beams with a plurality ofdata packets by communicating plurality of a control signals to the basestation to form the communication beams using at least one link from afirst base station and a second link through a second of the basestation.
 21. A method of operating a communication system having agateway station and a plurality base station comprising: dividing acommunication signal into a plurality of multiple dynamic links at thegateway station; directing the multiple dynamic links to a plurality ofbase stations; and coupling the multiple dynamic links through theplurality of base stations.
 22. A method as recited in claim 21 furthercomprising canceling interference between said multiple dynamic links.